Tilting pad bearing assemblies, and bearing apparatuses and methods of using the same

ABSTRACT

Embodiments disclosed herein are directed to tilting pad bearing assemblies, bearing apparatuses including the tilting pad bearing assemblies, and methods of using the bearing apparatuses. The tilting pad bearing assemblies disclosed herein include a plurality of tilting pads. At least some of the superhard tables exhibit a thickness that is at least about 0.120 inch and/or at least two layers having different wear and/or thermal characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/589,852 filed on Oct. 1, 2019, which is a continuation of U.S.application Ser. No. 15/747,706 filed on 25 Jan. 2018 (now issued asU.S. Pat. No. 10,473,154), which is a U.S. National Stage of PCTInternational Application No. PCT/US2016/045053 filed on 8 Aug. 2016,which claims priority to U.S. Provisional Application No. 62/210,301filed on 26 Aug. 2015, the disclosure of each of which is incorporatedherein, in its entirety, by this reference.

BACKGROUND

Wear-resistant, superhard compacts are utilized in a variety ofmechanical applications. For example, polycrystalline diamond compacts(“PDCs”) are used in drilling tools (e.g., cutting elements, gagetrimmers, etc.), machining equipment, bearing apparatuses, wire-drawingmachinery, and in other mechanical apparatuses.

PDCs and other superhard compacts have found particular utility assuperhard bearing elements in thrust bearings within pumps, turbines,subterranean drilling systems, motors, compressors, generators,gearboxes, and other systems and apparatuses. For example, a PDC bearingelement typically includes a superhard polycrystalline diamond layerthat is commonly referred to as a polycrystalline diamond (“PCD”) table.The PCD table can be formed and bonded to a substrate using ahigh-pressure/high-temperature (“HPHT”) process. Typically, thethickness of the PCD table is less than about 0.080 inch to minimize themoment and/or shear forces applied to the PCD table and minimizemanufacturing costs.

A bearing apparatus (e.g., a thrust-bearing apparatus) typicallyincludes a number of superhard bearing elements affixed to a supportring. The superhard bearing elements (e.g., a PDC bearing element) bearagainst another superhard bearing element(s) of an opposing bearingassembly during use. Superhard bearing elements are typically brazeddirectly into corresponding preformed recesses formed in a support ringof a fixed-position thrust bearing.

Despite the availability of a number of different bearing apparatusesincluding such PDCs and/or other superhard materials, manufacturers andusers of bearing apparatuses continue to seek bearing apparatuses thatexhibit improved performance characteristics, lower cost, or both.

SUMMARY

Embodiments disclosed herein are directed to tilting pad bearingassemblies, bearing apparatuses including the tilting pad bearingassemblies, and methods of using the bearing apparatuses. As will bediscussed in more detail herein, the tilting pad bearing assembliesinclude a plurality of tilting pads. A superhard table of at least someof the tilting pads include a superhard bearing surface and a lowersurface that is generally opposite the superhard bearing surface, withthe superhard table exhibiting a thickness (e.g., maximum thickness)that is at least about 0.120 inch and/or at least two layers havingdifferent wear and/or thermal characteristics. Such tilting pads mayincrease heat dissipation from the superhard table; increase a thicknessof a fluid film between the superhard bearing surface and an opposingbearing surface; help maintain such fluid film; increase one or more ofabrasion resistance, thermal resistance, impact resistance, or toughnessof the superhard table; improve the bonding between the superhard tableand another surface (e.g., a surface of a substrate), or combinationsthereof.

In an embodiment, a tilting pad bearing assembly is disclosed. Thetilting pad bearing assembly includes a support ring. The tilting padbearing assembly further includes a plurality of tilting padsdistributed circumferentially about an axis. The plurality of tiltingpads are also tilted and/or tiltably secured relative to the supportring. Each of the plurality of tilting pads includes a superhard tableincluding a superhard bearing surface, a lower surface, and at least oneperipheral surface extending between the superhard bearing surface andthe lower surface. The superhard table of at least some of the pluralityof tilting pads includes at least one of a thickness that is at leastabout 0.120 inch or a lower layer extending from the lower surfacetowards the superhard bearing surface and an upper layer extending fromat least a portion of the superhard bearing surface towards the lowersurface. The upper layer exhibits a greater abrasion resistance than thelower layer.

In an embodiment, a bearing apparatus is disclosed. The bearingapparatus includes a first bearing assembly. The first bearing assemblyincluding a first support ring. The first bearing assembly furtherincludes one or more bearing elements distributed circumferentiallyabout an axis. The one or more bearing elements include a bearingsurface. The one or more bearing elements are secured to the firstsupport ring. The bearing apparatus further includes a second bearingassembly. The second bearing assembly includes a second support ring.The second bearing assembly further includes a plurality of tilting padsdistributed circumferentially about an axis. The plurality of tiltingpads are also tilted and/or tiltably secured relative to the firstsupport ring. Each of the plurality of tilting pads includes a superhardtable including a superhard bearing surface, a lower surface, and atleast one peripheral surface extending between the superhard bearingsurface and the lower surface. The superhard table of at least some ofthe plurality of tilting pads includes at least one of a thickness thatis at least about 0.120 inch or a lower layer extending from the lowersurface towards the superhard bearing surface and an upper layerextending from at least a portion of the superhard bearing surfacetowards the lower surface. The upper layer exhibits a greater abrasionresistance than the lower layer.

In an embodiment, a method of operating a bearing apparatus isdisclosed. The method includes rotating a rotor relative to a stator. Atleast one of the stator or the rotor includes a first support ring andone or more bearing elements distributed circumferentially about anaxis. The one or more bearing elements include a bearing surface. Theone or more bearing elements are secured to the first support ring. Theother of the stator or the rotor includes a second support ring and aplurality of tilting pads distributed circumferentially about the axis.The plurality of tilting pads are also tilted and/or tiltably securedrelative to the first support ring. Each of the plurality of tiltingpads includes a superhard table including a superhard bearing surface, alower surface, and at least one peripheral surface extending between thesuperhard bearing surface and the lower surface. The superhard table ofat least some of the plurality of tilting pads includes at least one ofa thickness that is at least about 0.120 inch or a lower layer extendingfrom the lower surface towards the superhard bearing surface and anupper layer extending from at least a portion of the superhard bearingsurface towards the lower surface. The upper layer exhibits a greaterabrasion resistance than the lower layer.

Features from any of the disclosed embodiments may be used incombination with one another, without limitation. In addition, otherfeatures and advantages of the present disclosure will become apparentto those of ordinary skill in the art through consideration of thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate several embodiments of the present disclosure,wherein identical reference numerals refer to identical or similarelements or features in different views or embodiments shown in thedrawings.

FIGS. 1A and 1B are isometric and isometric cutaway views, respectively,of a tilting pad thrust-bearing assembly, according to an embodiment.

FIGS. 1C and 1D are isometric and cross-sectional views, respectively,of one of the plurality of tilting pads shown in FIGS. 1A and 1B,according to an embodiment.

FIG. 1E is an isometric cutaway view of a tilting pad thrust-bearingassembly, according to an embodiment.

FIG. 2 is an isometric cutaway view of a tilting pad thrust-bearingassembly, according to an embodiment.

FIG. 3A is an isometric cutaway view of a tilting pad thrust-bearingassembly, according to an embodiment.

FIG. 3B is an isometric cutaway view of a tilting pad thrust-bearingassembly, according to an embodiment.

FIGS. 4A and 4B are isometric and isometric cutaway views, respectively,of an opposing thrust-bearing assembly including a substantiallycontinuous bearing element, according to an embodiment.

FIGS. 5A and 5B are isometric cutaway and side cross-sectional views,respectively, of a thrust-bearing apparatus, according to an embodiment.

FIG. 6 is an exploded isometric view of a radial bearing apparatus,according to an embodiment.

FIG. 7 is a schematic isometric cutaway view of a subterranean drillingsystem that employs any of the bearing apparatuses disclosed herein,according to an embodiment.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to tilting pad bearingassemblies, bearing apparatuses including such tilting pad bearingassemblies, and methods of using such bearing apparatuses. As will bediscussed in more detail herein, the tilting pad bearing assembliesinclude a plurality of tilting pads. A superhard table of at least someof the tilting pads include a superhard bearing surface and a lowersurface that is generally opposite the superhard bearing surface, withthe superhard table exhibiting a thickness (e.g., maximum thickness)that is at least about 0.120 inch and/or include at least two layershaving different wear and/or thermal characteristics. Such tilting padsmay increase heat dissipation from the superhard table; increase athickness of a fluid film between the superhard bearing surface and anopposing bearing surface; help maintain such fluid film; increase one ormore of abrasion resistance, thermal resistance, impact resistance, ortoughness of the superhard table; improve the bonding between thesuperhard table and another surface (e.g., a surface of a substrate), orcombinations thereof.

The embodiments of tilting pad bearing assemblies and bearingapparatuses disclosed herein may be employed in subterranean drillingassemblies, pumps, compressors, turbo expanders, or other mechanicalsystems. Motor assemblies including at least one such bearing assemblyor bearing apparatus are also disclosed, as well as methods offabricating and using such bearing assemblies and bearing apparatuses.

While the description herein provides examples relative to asubterranean drilling and motor assembly, the tilting pad bearingassembly and apparatus embodiments disclosed herein may be used in anynumber of applications. For example, the bearing assemblies andapparatuses may be used in a pump, turbine bearing apparatus, motor,compressor, generator, gearbox, and other systems and apparatuses, or inany combination of the foregoing. Furthermore, the bearing assembliesand apparatuses may also be operated in hydrodynamic, or mixed-mode orboundary (e.g., rubbing or sliding) lubrication regimes, if desired orneeded.

FIGS. 1A and 1B are isometric and isometric cutaway views, respectively,of a tilting pad thrust-bearing assembly 100, according to anembodiment. The thrust-bearing assembly 100 includes a support ring 102and a plurality of tilting pads 104 tilted and/or tiltably secured tothe support ring 102. The tilting pads 104 may be distributedcircumferentially about a thrust axis 106. Each of the tilting pads 104may include a superhard table 108. The superhard table 108 may include asuperhard bearing surface 110, a lower surface 112 generally oppositethe superhard bearing surface 110, and at least one peripheral surface114 extending therebetween. At least some of (e.g., all of) thesuperhard tables 108 may include a thickness (e.g., maximum thickness)between the superhard bearing surface 110 and the lower surface 112 thatis at least about 0.120 inch.

In an embodiment, the support ring 102 may include a channel 116 and thetilting pads 104 may be at least partially placed within the channel116. The tilting pads 104 may be tilted and/or tiltably secured relativeto the support ring 102 in any suitable manner. For example, asdiscussed hereafter, a pivotal connection may be used to secure thetilting pads 104 to the support ring 102, although any other suitablesecurement or attachment mechanism may also be utilized. The supportring 102 may include an inner, peripheral surface 117 defining a hole118. The hole 118 may be generally centered about the thrust axis 106,and may be adapted to receive a shaft (e.g., a downhole drilling motorshaft, not shown).

The support ring 102 may be made from a variety of different materials.For example, the support ring 102 may be formed of steel, carbon steel,stainless steel, copper (e.g., brass or bronze alloys), tungstencarbide, another suitable material, or combinations thereof.

The tilting pads 104 may include at least one of fixed tilting pads,adjustable tilting pads, self-establishing tilting pads, other bearingpads or elements, or combinations thereof. In an embodiment, each of thetilting pads 104 may be located circumferentially adjacent to anothertilting pad 104 with a circumferential space or other offsettherebetween. For example, the circumferential space may be about 2.0 mmto about 20.0 mm. In an embodiment, the thrust-bearing assembly 100 mayinclude 3 to 20 tilting pads, such as 5 to 12, or 10 to 18 tilting pads.

In an embodiment, each of the tilting pads 104 may include a superhardbearing element 120 defining the superhard table 108 including thesuperhard bearing surface 110. Collectively, the superhard bearingsurfaces 110 of the tilting pads 104 may provide a substantiallynon-continuous superhard bearing surface of the thrust-bearing assembly100. In an embodiment, each superhard bearing surface 110 may exhibit agenerally truncated pie-shaped geometry, a generally circular geometry(e.g., generally cylindrical geometry), or a generally trapezoidalgeometry. However, in other embodiments, each superhard bearing surface110 may exhibit any suitable geometry.

As previously discussed, each of the plurality of tilting pads 104includes the superhard table 108 that includes at least one superhardmaterial. As used herein, the term “superhard” means a material having ahardness at least equal to the hardness of tungsten carbide. In anembodiment, the superhard material may include polycrystalline cubicboron nitride, polycrystalline diamond (e.g., formed by chemical vapordeposition or by HPHT sintering), diamond crystals, silicon carbide,silicon nitride, tantalum carbide, tungsten carbide (e.g., binderlesstungsten carbide, cobalt-cemented tungsten carbide), boron carbide,other metal carbides, other superhard ceramic carbides, or combinationsthereof. In another embodiment, the superhard material may include areaction-bonded superhard ceramic, such as reaction-bonded siliconnitride, reaction-bonded silicon carbide, or another suitablereaction-bonded superhard ceramic. The reaction-bonded superhard ceramicmay have additional materials at least partially embedded therein. Forexample, the additional materials may include diamond, polycrystallinediamond, cubic boron nitride, a material exhibiting a hardness greaterthan the reaction-bonded superhard ceramic, a material exhibiting athermal conductivity greater than the reaction-bonded superhard ceramic,or combinations thereof. For example, diamond may be added to thereaction-bonded superhard ceramic in an amount less than about 80 weight% (e.g., about 80 weight % to about 50 weight %, about 50 weight % toabout 25 weight %, less than about 25 weight %). The additionalmaterials in the reaction-bonded superhard ceramic may improve a thermalconductivity and/or a wear resistance of the superhard bearing element120. In an embodiment, the superhard bearing surface 110 may include asuperhard coating applied to a superhard or non-superhard material.

In some instances, high loads on the superhard bearing elements 120 maycause the superhard tables 108 and, in particular, the superhard bearingsurfaces 110 to exhibit relatively high temperatures during operation.In some embodiments, the relatively high temperatures may degrade and/ordeteriorate the superhard table 108. Degrading and/or deteriorating thesuperhard table 108 may lead to failure of the corresponding superhardbearing element 120 and the thrust-bearing assembly 100. For example,the superhard table 108 may include a PCD table. The PCD table maydegrade under certain operating conditions at temperatures greater thanabout 700° C. Additionally, the relatively high temperatures of thesuperhard table 108 may degrade or prevent formation of a fluid filmbetween the superhard bearing surface 110 and an opposing bearingsurface. Degrading or preventing the formation of the fluid film mayincrease contact between the superhard bearing surface 110 and theopposing bearing surface. Increased contact between the superhardbearing surface 110 and the opposing bearing surface may increase wearon the superhard bearing surface 110 and may further increase thetemperature of the superhard bearing element 120. Therefore, thesuperhard bearing elements 120 may be configured to exhibit relativelylow temperatures (e.g., less than 700° C.) during operation.

In some embodiments, the superhard bearing elements 120 may beconfigured to exhibit relatively low temperatures during operation byincreasing heat dissipation from the superhard table 108 thereof. In anembodiment, increasing the thickness of the superhard table 108 mayincrease the heat dissipated from the superhard table 108 during use.For example, the increased thickness of the superhard table 108 mayincrease a surface area of the superhard table 108 exposed to a coolingmedium (e.g., a lubricating fluid, drilling mud, etc.), therebyincreasing the heat dissipated from the superhard bearing element 120during operation. In some embodiments, the superhard table 108 may havea thickness (e.g., measured from the superhard bearing surface 110 tothe lower surface 112) of about 0.120 inch to about 0.140 inch, about0.120 inch to about 0.187 inch, about 0.120 inch to about 0.312 inch,about 0.156 inch to about 0.250 inch, or about 0.250 inch to about 0.312inch. In some embodiments, the superhard table 108 may have a thicknessthat is at least about 0.120 inch, at least about 0.200 inch, at leastabout 0.3 inch, at least about 0.4 inch, at least about 0.5 inch, about0.50 inch to about 0.75 inch, or at least about 0.75 inch.

Compared to a relatively thin superhard table (e.g., a superhard tablehaving a thickness less than about 0.120 inch and, in particular, lessthan about 0.080 inch), the superhard table 108 exhibiting a thicknessthat is at least about 0.120 inch may exhibit increased heat dissipationtherefrom. The increased heat dissipation of the superhard table 108 maylead to an increased load-bearing capacity of the thrust-bearingassembly 100, increased life expectancy of the superhard bearingelements 120 and the thrust-bearing assembly 100, and/or a thicker fluidfilm between the superhard bearing surface 110 and an opposing bearingsurface. However, increasing the thickness of superhard table 108 may becostly and/or may increase moment and/or shear forces experienced by thesuperhard bearing elements 120. Accordingly, the thickness of thesuperhard table 108 may vary from one embodiment to the next. Morespecifically, among other things, the thickness of the superhard table108 may depend on the overall size of the thrust-bearing assembly 100and/or of the superhard bearing elements 120, the particle size of thepolycrystalline diamond, the superhard material, amount that the bearingsurface protrudes from the support ring 102, the bearing loads, the typeof cooling medium, the number of start-ups and shut-downs of a systememploying the thrust-bearing assembly 100, or combinations thereof.

In an embodiment, the superhard table 108 may be configured to have amaximum thickness at and/or near a peripheral surface 114 of thesuperhard table 108. Accordingly, increasing the maximum thickness ofthe superhard table 108 may increase the surface area of the peripheralsurface 114, which may increase the overall exposure of the superhardtable 108 to the cooling medium.

The superhard table 108 may include at least one superhard materialexhibiting a relatively high thermal conductivity. The relatively highthermal conductivity may enable the superhard table 108 to dissipateheat from the superhard bearing surface 110 and the peripheral surface114. In an embodiment, a superhard material exhibiting a relatively highthermal conductivity may include a superhard material exhibiting athermal conductivity of about 100 W/m·K or greater. In anotherembodiment, the superhard table 108 may include a superhard materialexhibiting an ultra-high thermal conductivity. A superhard materialexhibiting an ultra-high thermal conductivity may include any superhardmaterial exhibiting a thermal conductivity of about 500 W/m·K orgreater, such as about 700 W/m·K or greater, or about 1000 W/m·K orgreater. For example, PCD may exhibit an ultra-high thermalconductivity. In an embodiment, the superhard table 108 may include asuperhard material exhibiting a thermal conductivity greater than atleast one of the thermal conductivity of the support ring 102, anotherpart of the superhard bearing element 120 (e.g., substrate 122), oranother part of the tilting pad 104 (e.g., support plate 124).

In an embodiment, the superhard table 108 may be configured such thatthe superhard bearing surface 110 is substantially planar andsubstantially parallel to the lower surface 112. In such an embodiment,the thickness of the superhard table 108 may be substantially uniformtherethrough and approximately equal to the maximum thickness of thesuperhard table 108. For example, the maximum thickness of the superhardtable 108 may be at or near the peripheral surface 114 to therebyincrease a surface area of the superhard table 108 that is exposed tothe lubricating fluid during use.

In an embodiment, the superhard table 108 may be configured such thatthe superhard bearing surface 110 is not substantially parallel with thelower surface 112 of the superhard table 108. In particular, thesuperhard table 108 may be configured such that the thickness of thesuperhard table 108 varies (e.g., the superhard bearing surface 110 issubstantially planar and the lower surface 112 is non-planar). Forexample, the relatively thick superhard table 108 may include a portionexhibiting a thickness that is at least about 0.120 inch and anotherportion exhibiting a thickness less than about 0.120 inch. In anembodiment, the maximum thickness of the superhard table 108 may be ator near at least a portion of the peripheral surface 114 of thesuperhard table 108. In an embodiment, the maximum thickness of thesuperhard table 108 may be spaced from the at least one peripheralsurface 114 of the superhard table 108. For example, in someembodiments, the lower surface 112 may extend between the at least oneperipheral surface 114 of the superhard table such that the lowersurface 112 forms a portion of a generally concave or convex cylindricalsurface, a portion of a generally concave or convex spherical surface, agenerally concave or convex conical surface, a stepped geometry, orother suitable geometry. Maximizing the surface area of the lowersurface 112 may enable the superhard table 108 to strengthen the bondwith the substrate 122 and increase the amount of heat dissipated fromthe superhard table 108 to an object contacting the lower surface 112 ofthe superhard table 108 (e.g., the substrate 122, the support plate 124,or the support ring 102). Further details and examples describing howthe lower surface 112 may extend between the at least one peripheralsurface 114 of the superhard table 108 are disclosed in U.S. Pat. No.9,080,385, the disclosure of which is incorporated herein, in itsentirety, by this reference. Any of the embodiments disclosed in U.S.Pat. No. 9,080,385 may be used in combination with the features and/orembodiments disclosed herein.

In an embodiment, the superhard bearing elements 120 may exhibit a shapethat is configured to increase its surface area to volume ratio. Therelatively increased surface area to volume ratio may increase the heatdissipated from the superhard table 108. For example, the superhardtable 108 may exhibit a single peripheral surface 114 (e.g., followingor forming a generally cylindrical surface). Increasing the thickness ofthe superhard table 108 and the single peripheral surface 114 mayincrease the exposed surface area of the superhard table 108. In anembodiment, the superhard table 108 may include two or more peripheralsurfaces 114, (e.g., following or forming a generally triangular shape,a generally rectangular shape, a generally trapezoidal shape, or anyother suitable peripheral shape). The two or more peripheral surfaces114 may further increase the exposed surface area of the superhard table108. Additionally, the superhard table 108 may include sharp, chamfered,or curved edges between the two peripheral surfaces 114 to furtherincrease the exposed surface area of the superhard table 108. In anembodiment, the at least one peripheral surface 114 may include one ormore features formed therein configured to increase the exposed surfacearea of the superhard table 108. In particular, at least a portion ofthe at least one peripheral surface 114 may include one or more features(e.g., ridges, notches, slots, dimples, recesses, etc.) configured toincrease the exposed surface area of the superhard table 108.

In some embodiments, the relatively thick superhard tables 108 mayincrease the expected life of the thrust-bearing assembly 100 andthrust-bearing apparatuses using the same. For example, the increasedheat dissipation of the relatively thick superhard tables 108 mayimprove the quality of the fluid film between the superhard bearingsurfaces 110 and an opposing bearing surface. In particular, theincreased heat dissipation may enable a thicker, more uniform, and/ormore consistent fluid film to form between the superhard bearingsurfaces 110 and the opposing bearing surface. As such, the improvedfluid film may decrease the amount of contact between the superhardbearing surfaces 110 and the opposing bearing surface. The decreasedcontact between the bearing surfaces may decrease wear on the superhardbearing surfaces 110 and may decrease heat generated by the superhardbearing elements 120.

In some embodiments, the relatively thick superhard tables 108 mayincrease the performance of the thrust-bearing assembly 100. Forexample, the relatively thick superhard tables 108 may enable thethrust-bearing assembly to increase the load bearing capacity thereof.In particular, the higher bearing capacities may cause the superhardbearing surfaces 110 of each of the superhard bearing elements 120 tocontact an opposing bearing surface. Contacting the superhard bearingsurfaces 110 against the opposing bearing surface may generateadditional heat. The relatively thick superhard tables 108 may increasethe heat dissipated therefrom compared to relatively less thicksuperhard tables. In an embodiment, as discussed above, the increasedheat dissipation may improve the quality of a fluid film between thesuperhard bearing surfaces 110 and the opposing bearing surface. Assuch, the thick superhard tables 108 may improve the performance (e.g.,increase load bearing capacity) and/or the life (e.g., prevents orinhibits overheating, uneven heating, or wear) of the thrust-bearingassembly 100 and thrust-bearing apparatuses using the same.

Referring to FIG. 1B, the superhard table 108 of the superhard bearingelement 120 may be bonded to the substrate 122. In an embodiment, thesuperhard bearing element 120 may be a PDC. The PDC may include a PCDtable bonded to the substrate 122. The PCD table includes a plurality ofdirectly bonded-together diamond grains exhibiting diamond-to-diamondbonding therebetween (e.g., sp³ bonding), which define a plurality ofinterstitial regions. A portion of, or substantially all of, theinterstitial regions of the PCD table may include a metal-solventcatalyst (e.g., iron, nickel, cobalt, or alloys thereof) and/or ametallic infiltrant disposed therein that is infiltrated from thesubstrate 122 or from another source during fabrication. The PCD tablemay further include thermally-stable diamond in which the metal-solventcatalyst and/or another infiltrant has been at least partially removedfrom a volume of the PCD table.

In an embodiment, the PDC may be formed, for example, by placing diamondparticles adjacent to the substrate 122 to form an assembly. The amountof diamond particles may be sufficient to form a relatively thick PCDtable. The assembly may be subject to HPHT process to form the PCD tableand bond the PCD table to the substrate 122, thereby forming the PDC.The temperature of the HPHT process may be at least about 1000° C.(e.g., about 1200° C. to about 1600° C.) and the cell pressure of theHPHT process may be at least about 4.0 GPa (e.g., at least about 7.5GPa, about 5.0 GPa to about 12 GPA, or about 7.5 GPa to about 11 GPa)for a time sufficient to sinter the diamond particles. During the HPHTprocess, a metal-solvent catalyst (e.g., cobalt, iron, nickel, or alloysthereof) may infiltrant the diamond grains from the substrate 122 tocatalyze formation of diamond-to-diamond bonding (e.g., sp³) between thediamond grains and bond the PCD table to the substrate 122. The bondedtogether diamond grains may define a plurality of interstitial regionstherebetween that may be at least partially occupied by themetal-solvent catalyst. In some embodiments, the PDC may be furtherprocessed to include a thermally-stable PCD table.

The diamond particles used to form the PCD table may exhibit an averageparticle size of about 50 μm or less, such as about 40 μm or less, about30 μm or less, about 20 μm or less, about 10 μm to about 18 μm, or about15 μm to about 18 μm. In some embodiments, the average particle size ofthe diamond particles may be about 10 μm or less, such as about 2 μm toabout 5 μm or submicron. In some embodiments, the diamond particles maycomprise a relatively larger size and at least one relatively smallersize. As used herein, the phrases “relatively larger” and “relativelysmaller” refer to particle sizes (by any suitable method) that differ byat least a factor of two (e.g., 30 μm and 15 μm). According to variousembodiments, the mass of diamond particles may include a portionexhibiting a relatively larger size (e.g., 40 μm, 30 μm, 25 μm, 20 μm,15 μm, 12 μm, 10 μm, 8 μm) and another portion exhibiting at least onerelatively smaller size (e.g., 6 μm, 5 μm, 4 μm, 3 μm, 2 μm, 1 μm, 0.5μm, less than 0.5 μm, 0.1 μm, less than 0.1 μm). In one embodiment, thediamond particles may include a portion exhibiting a relatively largersize between about 10 μm and about 40 μm and another portion exhibitinga relatively smaller size between about 1 μm and 4 μm. In someembodiments, the diamond particles may comprise three or more differentsizes (e.g., one relatively larger size and two or more relativelysmaller sizes), without limitation. In other embodiments, the diamondparticles may exhibit a single mode or bimodal size distribution (e.g.,a single mode or any of the foregoing sizes). The PCD table so-formedafter sintering may exhibit an average diamond grain size that is thesame or similar to any of the foregoing diamond particle sizes anddistributions.

More details about diamond particle sizes and diamond particle sizedistributions that may be employed are disclosed in U.S. patentapplication Ser. No. 13/734,354; U.S. Provisional Patent Application No.61/948,970; and U.S. Provisional Patent Application No. 62/002,001. Thedisclosures of each of U.S. patent application Ser. No. 13/734,354; U.S.Provisional Patent Application No. 61/948,970; and U.S. ProvisionalPatent Application No. 62/002,001 are incorporated herein, in theirentirety, by this reference.

In an embodiment, the superhard table 108 may be integrally formed withthe substrate 122. For example, the superhard table 108 may be asintered PCD table that is integrally formed with the substrate 122. Inan embodiment, the superhard table 108 may be a pre-formed superhardtable that has been HPHT bonded to the substrate 122 or otherwise bondedto the substrate 122 in a non-HPHT process such as brazing. For example,the superhard table 108 may be a pre-formed PCD table that has beenleached to substantially completely remove the metal-solvent catalystused in the HPHT sintering thereof and subsequently HPHT bonded orbrazed to the substrate 122 in a separate process.

In some embodiments, the superhard table 108 may be leached to depleteat least a portion of a catalyst or a metallic infiltrant therefrom inorder to enhance the thermal stability of the superhard table 108. Forexample, when the superhard table 108 is a PCD table, the superhardtable 108 may be leached to remove at least a portion of a metal-solventcatalyst from a region thereof to a selected depth to form a leachedthermally-stable region. The leached thermally-stable region may extendinwardly from the superhard bearing surface 110 to a selected depth. Inan embodiment, the depth of the thermally-stable region may be about 10μm to about 600 μm. More specifically, in some embodiments, the selecteddepth is about 50 μm to about 100 μm, about 100 μm to about 350 μm, orabout 350 μm to about 600 μm. The leaching may be performed in asuitable acid, such as aqua regia, nitric acid, hydrofluoric acid, ormixtures of the foregoing.

In an embodiment, the PDC formed in the HPHT process may be machinedsuch that the superhard bearing surface 110 exhibits a selected geometry(e.g., generally truncated pie-shaped geometry). For example, the PDCmay be machined using electrical discharge machining (e.g., wireelectrical discharge machining), a laser, or any other suitablemachining process. The PDC may be machined before or after the superhardtable 108 is at least partially leached.

The substrate 122 may be formed from any number of materials, and may beintegrally formed with, or otherwise bonded or connected to, thesuperhard table 108. Materials suitable for the substrate 122 mayinclude, without limitation, cemented carbides, such as tungstencarbide, titanium carbide, chromium carbide, niobium carbide, tantalumcarbide, vanadium carbide, or combinations thereof cemented with iron,nickel, cobalt, or alloys thereof. For example, in an embodiment, thesubstrate 122 comprises cobalt-cemented tungsten carbide. However, incertain embodiments, the substrate 122 may be omitted.

In the illustrated embodiment, each of the superhard bearing elements120 may be secured to a support plate 124 (FIG. 1B). The support plate124 may, for example, be formed of a metal, an alloy, a cemented carbidematerial, other material, or combinations thereof. In an embodiment, thesuperhard bearing elements 120 may be secured to the support plate 124by brazing, welding, mechanical fastening, press-fitting, anothersuitable method, or combinations thereof. In some embodiments, thesupport plate 124 may define a pocket into which the superhard bearingelements 120 may be tiltably or fixedly assembled and/or positioned. Inan embodiment, the support plate 124 has an integral construction suchthat a single body may form substantially the entire support plate 124.

Referring to FIG. 1D, in an embodiment, the superhard bearing elements120 may protrude from the support plate 124 in a manner that increasesexposure of at least a portion of the peripheral surface 114 of thesuperhard table 108 to a cooling medium. In other words, the superhardbearing elements 120 may have an exposed protruding portion that extendsabove a top surface 126 of the support plate 124 a distance 128(measured from the superhard bearing surface 110 to the top surface126), which is equal to, less than, or greater than the thickness of atleast a portion of the peripheral surface 114 of the superhard table(e.g., the entire thickness of the peripheral surface 114). Hence, insome embodiments, the distance 128 may be about 0.150 inch or more,about 0.120 inch or more, about 0.090 inch or more, such as about 0.090inch to about 0.20 inch, about 0.18 inch to about 0.030 inch, about0.025 inch to about 0.40 inch, about 0.30 inch to about 0.50 inch, orabout 0.50 inch or more. In other embodiments, the superhard bearingelements 120 may extend beyond the top surface 126 of the support plate124 to a distance 128 of about 0.90 or more multiplied by the maximumthickness of the superhard table 108 (e.g., a superhard table 108exhibiting a maximum thickness of about 0.20 inch may extend beyond thetop surface 126 by 0.18 inch or more). The distance 128 that thesuperhard bearing elements 120 extends beyond the top surface 126 of thesupport plate 124 may be selected to increase or maximize the surfacearea of the superhard table 108 exposed to the lubricating fluid. Forexample, the distance 128 that the superhard bearing elements 120 extendbeyond the top surface 126 may be selected based on the composition ofthe superhard table 108 (e.g., a stronger and/or tougher material mayextend a greater distance from the top surface 126 than a weaker and/orless tough material), the expected bearing capacity of thethrust-bearing assembly, the composition of the substrate 122, thestrength of the bond between the superhard table 108 and the substrate122, the maximum expected operating temperature of the superhard table108, the thermal conductivity of one or more components of thethrust-bearing assembly 100 (e.g., the substrate 122), or combinationsthereof.

In some embodiments, a portion of the peripheral surface 114 of thesuperhard table 108 may not protrude above the top surface 126 of thesupport plate 124 or only a relatively small portion of the peripheralsurface 114 may protrude about the top surface 126. In other words, aportion of the peripheral surface 114 may be in direct contact with oradjacent to the support plate 124. However, the portion of the supportplate 124 that is in direct contact with or adjacent to the supportplate 124 may still enhance heat dissipation from the superhard bearingelement 120. For example, heat can be dissipated from the peripheralsurface 114 of the superhard table 108 through the support plate 124.

In some embodiments, the tilting pad 104 may be configured such that thesubstrate 122 may also protrude above the top surface 126 of the supportplate 124. Exposing a peripheral surface 130 (FIG. 1C) of the substrate122 may increase the heat dissipated from the superhard table 108. Inparticular, the peripheral surface 130 of the substrate 122 may contactthe cooling medium that removes heat from the peripheral surface 130 ofthe substrate 122. For example, dissipating heat from the substrate 122may increase a temperature gradient between the superhard bearingsurface 110 and the substrate 122, thereby increasing the amount of heatdissipated from the superhard table 108 to the substrate 122. As such,the substrate 122 may protrude a distance (measured from the interfacebetween the superhard table 108 and the substrate 122 to the top surface126) that is greater than 0 inch, such as greater than about 0 inch toabout 0.10 inch, about 0.05 inch to about 0.20 inch, or about 0.20 inchor greater. As such, the substrate 122 may include a material configuredto dissipate heat from the superhard table 108, such as a materialexhibiting a thermal conductivity of about 100 W/m·K or greater. Thedistance the substrate 122 protrudes above the top surface 126 may beselected to increase or maximize the surface area of the substrate 122exposed to the cooling medium while accommodating the forces exerted onthe superhard bearing element 120.

In some embodiments, the thrust-bearing assembly 100 may be configuredto dissipate heat from the superhard bearing elements 120 via thesupport plate 124. For example, the support plate 124 may be thermallycoupled to the superhard table 108 either directly (e.g., a portion ofthe superhard table 108 directly contacts the support plate 124) orindirectly (e.g., through the substrate 122 and/or braze materialbetween support plate 124 and substrate 122). The support plate 124 mayalso include or be formed from a thermally conductive material, such ascopper or a copper alloy, to further help dissipate heat from thesuperhard table 108. At least a portion of the support plate 124 may beexposed to a cooling medium during operation of the thrust-bearingassembly 100. For example, the support plate 124 may be positioned inthe channel 116 to expose at least a portion of the support plate 124 tothe cooling medium. In an embodiment, the top surface 126 of the supportplate 124 may be exposed to the cooling medium.

The degree to which the tilting pads 104 rotate or tilt may be varied inany suitable manner. In an embodiment, the tilting pads 104 may betilted about respective radial axes that extend generally radiallyoutward from the thrust axis 106. In an embodiment, the support plate124 may be attached to a pin 132. The pin 132 may, for example, beformed of a metal, an alloy, a cemented carbide material, othermaterial, or any combinations thereof. The pin 132 may at leastpartially rotate, or may otherwise define or correspond to a tilt axis134. For example, the pin 132 may be journaled or otherwise securedwithin the support ring 102 in a manner that allows the support plate124 to rotate relative to the support ring 102. In some embodiments, thesupport plate 124 and/or the pin 132 may rotate or tilt from about zeroto about twenty degrees about the tilt axis 134. In some embodiments,the support ring 102 may be configured for bidirectional rotation. Insuch an embodiment, the pin 132 may be allowed to rotate in clockwiseand/or counter-clockwise directions. For example, the support plate 124and/or the pin 132 may rotate or tilt between a positive angle ornegative angle of about twenty degrees relative to the tilt axis 134.The one or more of the tilting pads 104 may be self-establishing orlimiting such that the tilting pads 104 may adjust or limit to a desiredtilt or other orientation based on the lubricant used, the axial forcesapplied along the thrust axis 106, the rotation speed of the runnerand/or the thrust-bearing assembly 100, other factors, or combinationsof the foregoing. In other embodiments, at least some of the tiltingpads 104 may be fixed at a particular tilt, or may be manually set to aparticular tilt with or without being self-establishing.

Further, the pin 132 represents one embodiment of a mechanism forfacilitating rotation, translation, or positioning of the tilting pads104. In other embodiments, leveling links, pivotal rockers, sphericalpivots, biasing elements, other elements, or any combination of theforegoing may also be used to tilt at least some of the tilting pads104. In an embodiment, the support plate 124 may be used to facilitaterotation or tilt of a respective tilting pad 104. For example, thesupport plate 124 may include a spherical pivot, pivotal rocker, orleveling link interface. In other embodiments, the support plate 124 maybe eliminated and the substrate 122 may be directly machined orotherwise formed to tilt at least some of the tilting pads 104. Examplesof tilting mechanisms that may be employed are disclosed in U.S. Pat.No. 8,967,871, the disclosure of which is incorporated herein, in itsentirety, by this reference.

FIGS. 1C and 1D are isometric and cross-sectional views, respectively,of one of the plurality of tilting pads 104 shown in FIGS. 1A and 1B,according to an embodiment. The tilting pad 104 may include a superhardbearing element 120. The superhard bearing element 120 may be secured toa support plate 124 by brazing, adhesives (e.g., high-temperatureadhesives), press-fitting, fastening with fasteners, or other suitableattachment mechanisms. In the illustrated embodiment, the support plate124 may facilitate attachment of the superhard bearing element 120 tothe support plate 124 by including an interior pocket 136. The interiorpocket 136 may be sized to generally correspond to a size of thesubstrate 122. It is noted that the support plate 124 merely representsone embodiment for a support plate and other configurations may be used.For example, the support plate 124 may lack a pocket or otherreceptacle.

In the illustrated embodiment, the superhard bearing surface 110 issubstantially planar, although such an embodiment is merelyillustrative. In other embodiments, the first superhard bearing surface110 may be curved, or have another contour or topography. Moreover,outer edges of the superhard bearing element 120 may optionally includea chamfer 138. The chamfer 138 may be formed by placing a chamfer thatextends between the superhard bearing surface 110 and the peripheralsurface 114.

FIG. 1E is an isometric partial cross-sectional view of a tilting padthrust-bearing assembly 100′, according to an embodiment. Thethrust-bearing assembly 100′ may be substantially similar to thethrust-bearing assembly 100 shown in FIGS. 1A and 1B. The support ring102 carries a plurality of first tilting pads 104A. The plurality offirst tilting pads 104A may be substantially similar to the tilting pads104 shown in FIGS. 1A-1D. For example, the plurality of first tiltingpads 104A may include a first superhard table 108A exhibiting a firstthickness (e.g., first maximum thickness). The first thickness may berelatively thick (e.g., at least about 0.120 inch). The first superhardtable 108A may be bonded to a substrate 122A. The first tilting pads104A may also include a support plate 124 secured to the substrate 122Aand a pin 132, though the support plate 124 and/or the pin 132 may beomitted.

The thrust-bearing assembly 100′ may also include a plurality of secondtilting pads 104B. The second tilting pads 104B include a secondsuperhard table 108B exhibiting a second thickness (e.g., second maximumthickness), the second thickness being different than the first maximumthickness. In an embodiment, the second thickness may be less than thefirst maximum thickness. For example, the second thickness may be lessthan about 0.120 inch, such as less than about 0.800 inch. The superhardtable 108B may be bonded to a substrate 122B. The second tilting pads104B may further include a support plate 124 having the substrate 122Bsecured thereto and a pin 132, though the support plate 124 and/or thepin 132 may be omitted.

The second tilting pads 104B may decrease the overall cost of thethrust-bearing assembly 100′ compared to a thrust-bearing assemblyconsisting entirely of the first tilting pads 104A. As such, thethrust-bearing assembly 100′ may include the benefits of the firsttilting pads 104A (e.g., increased performance and/or increased lifeexpectancy) while reducing costs.

Additionally, in some embodiments, certain portions of thethrust-bearing assembly 100′ may be more prominent (e.g., exposed to agreater load and/or wear) than other portions of the thrust-bearingassembly 100′. As such, the tilting pads at or near the more prominentportions of the thrust-bearing assembly 100′ may include the firsttilting pads 104A, while the remaining portions of the thrust-bearingassembly 100′ may include the second tilting pads 104B. In anembodiment, the second tilting pads 104B may include a material thatexhibits a higher operating temperature than the first tilting pads 104Aand, therefore, the second tilting pads 104B do not need to dissipateheat as efficiently as the first tilting pads 104A.

In an embodiment, the thrust-bearing assembly 100′ may include aplurality of third tilting pads (not shown). Each of the third tiltingpads may include a superhard table (not shown) exhibiting a thirdthickness (e.g., third maximum thickness) that is between the firstthickness and the second thickness. Similarly, the thrust-bearingassembly 100′ may include additional tilting pads (e.g., a plurality offourth tilting pads, a plurality of fifth tilting pads, etc.), whereeach of the additional titling pads exhibit a thickness (e.g., maximumthickness) that is different than the first, second, and thirdthicknesses.

FIG. 2 is an isometric cutaway view of a tilting pad thrust-bearingassembly 200, according to an embodiment. Except as otherwise disclosedherein, the thrust-bearing assembly 200 may be substantially similar tothe thrust-bearing assembly 100 shown in FIGS. 1A and 1B. For example,the thrust-bearing assembly 200 includes a support ring 202 configuredto carry a plurality of tilting pads 204. The support ring 202 may alsoinclude a channel 216 having the tilting pads 204 at least partiallypositioned therein. Each of the tilting pads 204 may include a superhardbearing element 220. Each tilting pad 204 may also include a supportplate 224 secured to a superhard bearing element 220 and a pin 232.However, in some embodiments, the support plate 224 and/or the pin 232may be omitted.

Each of superhard bearing elements 220 includes a superhard table 208.Each superhard table 208 may include any of the superhard materialsdisclosed herein. Each superhard table 208 also includes a superhardbearing surface 210, a generally opposing lower surface 212, and aperipheral surface 214 extending between the superhard bearing surface210 and the lower surface 212 In some embodiments, the superhard bearingelements 220 may include a substrate 222 bonded to the lower surface 212of the superhard table 208. The substrate 222 may include any of thesubstrate materials disclosed herein. For example, the superhard bearingelement 220 may include a PCD table bonded to a cobalt-cemented tungstencarbide substrate. Alternatively, the substrate 222 may be omitted.

Each superhard table 208 may include at least two layers, such as twolayers, three layers, or four or more layers. The at least two layersinclude at least an upper layer 240 and a lower layer 242. The upperlayer 240 extends from at least a portion of the superhard bearingsurface 210 (e.g., adjacent to the entire superhard bearing surface 210)for a selected distance (e.g., greater than about 250 μm, greater thanabout 500 μm) towards the lower surface 212. Similarly, the lower layer242 extends from the lower surface 212 for a selected distance towardsthe superhard bearing surface 210. In some embodiments, the lower layer242 may extend from the lower surface 212 to the upper layer 240,thereby forming an interface 244 between the upper layer and the lowerlayer 242. In other embodiments, the superhard table 208 may include atleast one intermediate layer (not shown) positioned between at least aportion of the upper layer 240 and at least a portion of the lower layer242. In such an embodiment, an interface may exist between the betweenthe intermediate layer and the upper layer 240 or the lower layer 242.In an embodiment, the intermediate layer may be formed by the mixing ofthe upper layer 240 and the lower layer 242 during formation of thesuperhard table 208 (e.g., during sintering). In one embodiment, theupper layer 240 and the lower layer 242 may include substantially thesame superhard material (e.g., PCD).

In some embodiments, the lower layer 242 is configured to act as atransition layer between the upper layer 240 and the substrate 222. Forexample, the lower layer 242 may be configured to be tougher than theupper layer 240 and/or configured to help moderate coefficient ofthermal expansion mismatch between the superhard table 208 and thesubstrate 222, which may enable the superhard table 208 to betterwithstand thermal strain (e.g., caused by heating and cooling thesuperhard bearing element 220). For example, the lower layer 242 may beformulated to exhibit a coefficient of thermal expansion that is lessthan the upper layer 240 and greater than the substrate 222. The atleast one intermediate layer may also be configured to act as atransition layer between the lower layer 242 and the upper layer 240.

In some embodiments, the upper layer 240 is configured to exhibit anabrasion resistance that is greater than the lower layer 242. Forexample, the upper layer 240 may include an upper average grain size andthe lower layer 242 may include a lower average grain size that isdifferent than the upper average grain size. The upper average grainsize may be selected such that the upper layer 240 exhibits an abrasionresistance that is greater than the lower layer 242. For example, theupper layer 240 may exhibit an abrasion resistance greater than thelower layer 242 by having the upper average grain size be greater thanthe lower average grain size. In another embodiment, the upper layer 240may exhibit an abrasion resistance greater than the lower layer 242 byhaving the upper average grain size be less than the lower average grainsize. Whether the upper layer 240 exhibits an upper average grain sizethat is greater than or less than the lower average grain size maydepend on the cooling medium, the superhard material of the upper layer240 and the lower layer 242, the configuration of the bearing surface ofthe opposing bearing assembly (e.g., the composition of the bearingsurface, a substantially continuous bearing surface or a substantiallynon-continuous bearing surface, etc.), the load on the tilting pads 204,etc.

The relative abrasion resistance between the upper layer 240 and thelower layer 242 may be evaluated using a vertical lathe test (e.g.,vertical turret lathe). For example, the relative abrasion resistancebetween the upper layer 240 and the lower layer 242 may be determinedusing a first cutting element including a first superhard table havingonly the upper layer 240 and a second cutting element including a secondsuperhard table having only the lower layer 242. The abrasion resistanceis determined by comparing a volume of workpiece cut and a volume of thecutting element worn away, using water as a coolant to cool theworkpiece, during the vertical lathe test. The relative abrasionresistance between the upper layer 240 and the lower layer 242 may bedetermined by evaluating the difference in the volume worn away betweenthe first superhard table of the first cutting element and the secondsuperhard table of the second cutting element. The more volume removedfrom one of the first or second superhard tables during the cutting testis an indication that it is relatively less abrasion resistant than theother one of the first or second superhard tables. An example ofsuitable parameters that may be used to determine the abrasionresistance of the upper layer 240 and the lower layer 242 are a depthcut for the cutting element of about 0.254 mm, a back rake angle for thecutting element of about 20 degrees, an in-feed for the cutting elementof about 6.35 mm/rev, a rotary speed of the workpiece to be cut of about101 rpm, and the workpiece may be made from Bane granite having a 914 mmouter diameter and a 254 mm inner diameter. In other embodiments, anysuitable test method for conducting abrasion resistance tests forsuperhard materials may be used. For example, the American Society forTesting and Materials (“ASTM”) has numerous standards that may besuitable for abrasion resistance testing of the upper layer 240 and thelower layer 242.

In an embodiment, the lower average grain size may be at least about 2times the size of the upper average grain size. In such an embodiment,the relatively coarse lower average grain size may increase thetoughness of the superhard table 208, while the relatively fine upperaverage grain size may increase an abrasion resistance of the superhardtable 208 and/or an impact resistance of the superhard table 208.Additionally, in some embodiments, the relatively coarse lower averagegrain size may improve the bond between the superhard table 208 and thesubstrate 222.

In an embodiment, the lower average grain size may be at least about 2.0times (e.g., about 2 times to about 3.5 times, 3.5 times to about 5times, or at least about 5 times) the size the upper average grain size.In particular, the lower average grain size may be at least about 20 μm,at least about 40 μm, at least about 50 μm, at least about 60 μm, about50 μm to about 75 μm, about 60 μm to about 80 μm, or greater than about80 μm; and the upper average grain size may be less than about 40 μm,such as about 10 μm to about 40 μm, 15 μm to about 35 μm, 20 μm to about35 μm, about 20 μm, about 30 μm, or less than about 10 μm. In otherembodiments, the lower average grain size may be less than about 20 μm.In other embodiments, the upper average grain size may be greater thanabout 40 μm so long as the lower average grain size is at least 2 timesthe size of the fine upper average grain size. It should be noted thatthe upper layer 240 and/or the lower layer 242 may exhibit bimodal orgreater particle size distributions. For example, the upper layer 240may exhibit a first average grain size of about 20 μm and the lowerlayer 242 may exhibit a second average grain size of about 2 μm.Examples of PDCs having more than one layer that may be used for thePDCs of the tilting pads disclosed herein are disclosed in U.S. Pat. No.8,297,382, the disclosure of which is incorporated herein, in itsentirety, by this reference.

In an embodiment, the upper layer 240 may exhibit a larger average grainsize than the average grain size of the lower layer 242. For example,the upper average grain size may be at least about 2 times the size ofthe lower average grain size. The relatively coarser upper average grainsize may increase the abrasion resistance and/or toughness of thesuperhard table 208, depending on the application of the thrust-bearingassembly 200. Additionally, the relatively finer lower average grainsize may improve the bond between the superhard table 208 and thesubstrate 222. The average grain size of the upper layer 240 may exhibitany of the disclosed grain sizes or diamond particle sizes, and thelower layer 242 may exhibit any of the disclosed grain sizes or diamondparticle sizes, without limitation.

In an embodiment, at least one additional material may be added to theupper layer 240 and/or the lower layer 242. The additional material mayinclude tungsten particles, tungsten carbide particles, sinteredcemented tungsten carbide particles, cobalt, iron, nickel, boron,combinations thereof, or any other suitable material. The additionalmaterial may be present in the upper layer 240 and/or lower layer 242 inan amount of about 1 weight % to about 20 weight %, such as about 1weight % to about 10 weight %, or about 5 weight % to about 15 weight %.For example, the additional material may include a mixture of about 1weight % to about 3 weight % cobalt and about 0.1 weight % to about 0.5weight % boron. In some embodiments, only one of the upper layer 240 orthe lower layer 242 may include the additional material while the otherlayer is substantially free of the additional material. In otherembodiments, a small amount of the additional material may migrate froma layer that includes the additional material to a layer that does notinclude the additional material. Examples of PDCs including a PCD tablehaving more than one layer that may be used for the PDCs of the tiltingpads disclosed herein are disclosed in U.S. Pat. No. 8,727,046, thedisclosure of which is incorporated herein, in its entirety, by thisreference.

In an embodiment, an interface (e.g., interface 244) between the upperlayer 240, the lower layer 242, and/or the at least one intermediatelayer may be substantially planar. For example, the superhard table 208may include an interface 244 between the upper layer 240 and the lowerlayer 242. The interface 244 may be substantially planar and may besubstantially parallel to at least a portion of (e.g., the entirety of)at least one of the superhard bearing surface 210 or the lower surface212. Alternatively, the interface 244 between the upper layer 240 andthe lower layer 242 may be nonplanar and/or may be substantiallynonparallel relative to at least a portion of (e.g., the entirety of)superhard bearing surface 210 and/or the lower surface 212. Thenonparallel interface 244 may cause the thickness of the upper layer 240(measured from the superhard bearing surface 210 to the interface 244)and/or the thickness of the lower layer 242 (measured from the interface244 to the lower surface 212) to vary. The thickness of the upper layer240 and the thickness of the lower layer 242 may be selected or designeddepending on the application of the thrust-bearing assembly 200. Forexample, certain portions of the superhard bearing surface 210 may bemore prominent than other portions of the superhard bearing surface 210.Portions of the upper layer 240 immediately below more prominentportions of the superhard bearing surface 210 may be thicker than otherportions of the upper layer 240.

In another embodiment, at least a portion of (e.g., an entirety of) aninterface between the upper layer 240, the lower layer 242, and/or theat least one intermediate layer may be substantially nonplanar. Forexample, the superhard table 208 may include an interface 244 betweenthe upper layer 240 and the lower layer 242. The interface 244 betweenthe upper layer 240 and the lower layer 242 may exhibit a generallyconcave (relative to the superhard bearing surface 310) or convexspherical geometry, or a generally concave or convex cylindricalgeometry. Alternatively, the interface 244 between the upper layer 240and the lower layer 242 may exhibit generally concave or convex conicalgeometry, a generally stepped geometry, generally ellipsoid geometry, oranother other suitable geometry. Such a nonplanar interface 244 mayenable the superhard table 208 to include portions exhibiting arelatively thick upper layer 240 and/or include portions exhibiting arelatively thick lower layer 242.

In an embodiment, the upper layer 240 may only extend from a portion ofthe superhard bearing surface 210. In such an embodiment, the lowerlayer 242 and/or the at least one intermediate layer may extend from aportion of the lower surface 212 to a portion of the superhard bearingsurface 210. For example, the upper layer 240 may exhibit a generallyannular cross-sectional geometry. In an embodiment, the upper layer 240may extend from a portion of the superhard bearing surface 210 and theat least one peripheral surface 214 towards the lower surface 212.

In an embodiment, at least one of the superhard bearing elements 220comprises a PDC. The PDC includes a PCD table bonded to a substrate 222.The PDC may be formed by positioning a plurality of first diamondparticles adjacent to substrate 222 and a plurality of second diamondparticles adjacent to the first diamond grains, thereby forming anassembly. The substrate 222 may include any of the substrates disclosedherein. The first diamond particles may exhibit a first pre-sinteredaverage particle size and the second diamond particles may exhibit asecond pre-sintered average particle size. In an embodiment, the firstpre-sintered average particle size may be at least 2 times the size ofthe second pre-sintered average particle size. The assembly may besubjected to an HPHT process similar to any of the HPHT processesdisclosed herein. The HPHT process may sinter the first diamondparticles to form the lower layer 242, sinter the second diamondparticles to form the upper layer 240, bond the lower layer 242 to theupper layer 240, and bond the lower layer 242 to the substrate 222. Theupper layer 240 exhibits an upper average grain size and the lower layer242 exhibits a lower average grain size that is at least 2 times thesize of the upper average grain size. In some embodiments, the upperaverage grain size and the lower average grain size may be differentthan the second pre-sintered average particle size and the firstpre-sintered average particle size, respectively. In some embodiments,the PCD table may be further processed to form a thermally-stable PCDtable (e.g., an at least partially leached PCD table).

In an embodiment, the upper layer 240 and the lower layer 242 may beformed in separate processes (e.g., preformed). For example, the upperlayer 240 may include a PCD table formed in a first HPHT process and thelower layer 242 may include a PCD table formed in a second HPHT process.The lower layer 242 may be bonded to the substrate 222 during the secondHPHT process or may be bonded to the substrate 222 in a subsequent step.The upper layer 240 may then be bonded to the lower layer 242 in a thirdHPHT process, a brazing process, during the second HPHT process, oranother suitable attachment process.

FIG. 3A is an isometric cutaway view of a tilting pad thrust-bearingassembly 300A, according to an embodiment. Except as otherwise disclosedherein, the thrust-bearing assembly 300A may be substantially similar tothe thrust-bearing assembly 100, shown in FIGS. 1A-2. For example, thethrust-bearing assembly 300A includes a support ring 302. Thethrust-bearing assembly 300A also includes a plurality of first tiltingpads 304A′ and a plurality of second tilting pads 304A″. The firsttilting pads 304A′ and the second tilting pads 304A″ may be tiltedand/or tiltably secured to the support ring 302.

The first tilting pads 304A′ may be substantially similar to the tiltingpads 104 shown in FIGS. 1A-1D. For example, the first tilting pads 304A′may each include a superhard bearing element 320A′ that includes arelatively thick superhard table 308A′ exhibiting a thickness (e.g.,maximum thickness) that is at least about 0.120 inch. The relativelythick superhard table 308A′ may exhibit an average grain size that issubstantially uniform throughout. The superhard table 308A′ may bebonded to a substrate 322 and define a superhard bearing surface 310A′.Each superhard bearing element 320A′ may be configured to moreefficiently dissipate heat from a superhard bearing surface 310A′ of thesuperhard table 308A′.

The second tilting pads 304A″ may be substantially similar to thetilting pads 204 shown in FIG. 2. For example, each of the secondtilting pads 304A″ may include a superhard bearing element 320A″ thatincludes a superhard table 308A″. The superhard table 308A″ includes atleast two layers, such as an upper layer 340A that extends from at leasta portion of a superhard bearing surface 310A towards a lower surface312 of the superhard table 308A″ and a lower layer 342A that extendsfrom the lower surface 312 towards the superhard bearing surface 310A″.In an embodiment, the upper layer 340A may exhibit an upper averagegrain size and the lower layer 342A may exhibit a lower average grainsize that is at least 2 times the size of the upper average grain size.As such, the upper layer 340A may exhibit at least one of improvedabrasion resistance, thermal resistance, and impact resistance.Optionally, the lower layer 342A may exhibit at least one of improvedtoughness or bonding between the lower layer 342A and a substrate 322.

In some embodiments, the first tilting pads 304A′ and the second tiltingpads 304A″ may improve the performance and/or life expectancy of thethrust-bearing assembly 300A. For example, during normal operation, thethrust-bearing assembly 300A may operate at sufficiently high rotationspeeds and/or sufficiently low loads that enable a fluid film to formbetween the superhard bearing surfaces 310A′ and 310A″ and an opposingbearing surface. The relatively thick superhard tables 308A′ of thefirst tilting pads 304A′ may maintain and thicken the fluid film betweenthe bearing surfaces, thereby improving the performance and/or lifeexpectancy of the thrust-bearing assembly 300A during hydrodynamicconditions. However, during start-ups and shut-downs of a systememploying the thrust-bearing assembly 300A, the superhard bearingsurfaces 310A′ and 310A″ may contact opposing bearing surfaces. As such,the improved abrasion resistance, thermal resistance, and/or impactresistance of the second tilting pads 304A″ and the improved heatdissipation of the first tilting pads 304A′ may improve the performanceand/or life expectancy of the thrust-bearing assembly 300A.

In an embodiment, the thrust-bearing assembly 300A may be modified toinclude a plurality of third tilting pads (not shown). In someembodiments, the third tilting pads may replace at least some of (e.g.,all of) the first tilting pads 304A′. In other words, the thrust-bearingassembly 300A may only include a plurality of second tilting pads 304A″and a plurality of third tilting pads. The third tilting pads may besubstantially similar to the first tilting pads 304A′ except that thethird tilting pads include a relatively thin superhard table exhibitinga thickness (e.g., maximum thickness) that is less than about 0.120 inch(e.g., less than about 0.080 inch). Additionally, in some embodiments,the third tilting pads may exhibit an average grain size that issubstantially uniform throughout. The third tilting pads may cost lessand/or may be easier to manufacture than the first tilting pads 304A′.

FIG. 3B is an isometric cutaway view of a tilting pad thrust-bearingassembly 300B, according to an embodiment. The tilting padthrust-bearing assembly 300B may be substantially similar to thethrust-bearing assembly 100 shown in FIGS. 1A-1B. For example, thethrust-bearing assembly 300B may include a plurality of tilting pads304B tilted and/or tiltably secured to the support ring 302. Eachtilting pad 304B may include a superhard bearing element 320B thatincludes a superhard table 308B. The superhard table 308B includes asuperhard bearing surface 310B and a lower surface 312B that generallyopposes the superhard bearing surface 310B. In some embodiments, thesuperhard bearing elements 320B may include a substrate 322 bonded tothe superhard table 308B (e.g., a PCD table bonded to the substrate322).

At least some of the superhard bearing elements 320B may include asuperhard table 308B exhibiting a thickness (e.g., maximum thickness)that is at least about 0.120 inch. Additionally, such superhard tables308B may include at least two layers, such as an upper layer 340Bextending from the superhard bearing surface 310B towards the lowersurface 312B and a lower layer 342B extending from the lower surface312B towards the superhard bearing surface 310B (e.g., to the upperlayer 340B).

At least some of (e.g., all of) the superhard bearing elements 320B ofthe thrust-bearing assembly 300B may include a superhard table 308Bhaving a thickness that is at least about 0.120 inch and at least twolayers. Such a thrust-bearing assembly 300 may exhibit improved theperformance and/or life expectancy compared to other thrust-bearingassemblies. For example, a tilting pad 304B including a superhard tablethat includes a thickness that is at least about 0.120 inch and at leasttwo layers may exhibit increased heat dissipation; better fluid filmsbetween the superhard bearing surface 310B and an opposing bearingsurface; at least one of improved abrasion resistance, thermalresistance, impact resistance, or toughness; improved bonding betweenthe lower surface 312B and a surface (e.g., a surface of the substrate322); or combinations thereof. One or more of these properties mayincrease the performance and/or life expectancy of the tilting pad 304Bto thereby increase the performance and/or life expectancy of thethrust-bearing assembly 300B.

In some embodiments, the thrust-bearing assembly 300B may include aplurality of additional tilting pads (not shown) that do not exhibit athickness that is at least about 0.120 inch and/or that do not includeat least two layers. For example, the additional tilting pads may besubstantially similar to at least one of the tilting pad 104 shown inFIGS. 1A-1D, tilting pad 104B shown in FIG. 1E, or tilting pad 204 shownin FIG. 2. The additional tilting pads may be relatively cheaper, easierto manufacture, or may include one or more additional feature thatimproves the performance thereof without being configured similar to thetilting pads 304B.

In an embodiment, the thrust-bearing assembly 300B may include at leasta first region that consists of tilting pads 304B that exhibit athickness that is about 0.120 inch and include at least two layers, anda second region that consists of any differently configured tilting pads(e.g., additional tilting pads as described above). For example, thefirst region may be more prominent that the second region. In anembodiment, the thrust-bearing assembly 300B may include a plurality oftilting pads 304B exhibiting a thickness that is about 0.120 inch and atleast two layers and any of the additional tilting pads interspersedwith each other. Such a configuration may improve performance and/orlife expectancy of the tilting pads 304B compared to a thrust-bearingassembly 300B that includes only the additional tilting pads.

FIGS. 4A and 4B are isometric and isometric cutaway views, respectively,of an opposing thrust-bearing assembly 446 including a substantiallycontinuous bearing element 448, according to an embodiment. Thethrust-bearing assembly 446 may include a support ring 450 having aninner peripheral surface 417 defining a hole 418 through which a shaft(not shown) may extend. The support ring 450 may be made from the samematerials as the support ring 102 provided in FIG. 1A. The support ring450 may include an annular slot 452 (FIG. 4B) configured to receive acorresponding substantially continuous bearing element 448.

The substantially continuous bearing element 448 may be attached to thesupport ring 450 in a fixed position. For example, the substantiallycontinuous bearing element 448 is at least partially received by theannular slot 452 and mounted to the support ring 450. The substantiallycontinuous bearing element 448 may be secured at least partially withinthe annular slot 452 of the support ring 450 by brazing, press-fitting,welding, using an adhesive, using mechanical fasteners, using anothersuitable technique, or combinations of the foregoing.

The substantially continuous bearing element 448 includes asubstantially continuous bearing surface 454. The substantiallycontinuous bearing surface 454 may comprise a superhard material (e.g.,a material having hardness greater than tungsten carbide), anon-superhard material (e.g., a material having a hardness less thantungsten carbide), or combinations thereof. For example, thesubstantially continuous bearing element 448 may comprise a superhardtable 456 (e.g., an unleached or an at least partially leached PCDtable) bonded to a substrate 458.

In an embodiment, the substantially continuous bearing element 448 maybe formed from a single element (e.g., a continuous bearing elementhaving a continuous bearing surface). In an embodiment, thesubstantially continuous bearing element 448 may include a plurality ofbearing elements that collectively form the substantially continuousbearing element 448 (e.g., a substantially continuous bearing elementhaving a substantially continuous bearing surface). In an embodiment,the thrust-bearing assembly 446 may include a plurality ofcircumferentially spaced bearing elements (e.g., sliding bearingelements) instead of the substantially continuous bearing element 448.Examples of substantially continuous bearing elements that include aplurality of bearing elements that may be used in combination withtilting pad bearing apparatuses disclosed herein are disclosed in U.S.Pat. No. 7,896,551. The disclosure U.S. Pat. No. 7,896,551 isincorporated herein, in its entirety, by this reference.

FIGS. 5A and 5B are isometric cutaway and side cross-sectional views,respectively, of a thrust-bearing apparatus 560, according to anembodiment. The thrust-bearing apparatus 560 may include athrust-bearing assembly that forms a stator 562 and another bearingassembly that forms a rotor 564. In the illustrated embodiment, thestator 562 includes a tilting-pad thrust-bearing assembly (e.g., thetilting pad thrust-bearing assembly 100, 100′, 200, 300A, or 300B) andthe rotor 564 includes an opposing thrust-bearing assembly (e.g., theopposing thrust-bearing assembly 446). The terms “rotor” and “stator”refer to rotating and stationary components of the thrust-bearingapparatus 560, respectively, although the rotating and stationary statusof the illustrated embodiment may also be reversed.

The stator 562 may include a support ring 502 and a plurality of tiltingpads 504 mounted or otherwise attached to the support ring 502. Thetilting pads 504 may include any of the tilting pads or tilting padfeatures disclosed herein (e.g., the tilting pads 104, 104A, 104B, 204,304A′, 304A″, 304B, etc.). For example, at least some of the tiltingpads 504 may exhibit a thickness (e.g., maximum thickness) that is about0.120 inch and/or at least two layers. Each of the tilting pads 504 maybe tilted and/or tilt relative to a rotational axis 506 of thethrust-bearing apparatus 560 and/or one or more surfaces of the supportring 502. The tilting pads 504 may be fixed at a particular tilt, may bemanually adjusted to exhibit a particular tilt, may self-establish at aparticular tilt, or may be otherwise configured.

The rotor 564 may include a support ring 550 and a substantiallycontinuous bearing element 548 mounted or otherwise secured to thesupport ring 550 (e.g., as described with respect to FIGS. 4A and 4B).The substantially continuous bearing element 548 includes asubstantially continuous bearing surface. The substantially continuousbearing surface is positioned generally adjacent to the superhardbearing surfaces (not shown) of the tilting pads 504. A fluid film 570(FIG. 5B) may develop between the substantially continuous bearingsurface and the superhard bearing surface of the tilting pads 504. Thesubstantially continuous bearing surface may be formed from the samematerials as the substantially continuous bearing surface 454 providedin FIGS. 4A and 4B.

As shown in FIG. 5A, a shaft 566 may be coupled to the support ring 550and operably coupled to an apparatus (e.g., a down hole drilling motor,not shown) capable of rotating the shaft 566 in a direction R (or in anopposite direction). For example, the shaft 566 may extend through andmay be secured to the support ring 550 of the rotor 564 by press-fittingor a threaded connection that couples the shaft 566 to the support ring550, or by using another suitable technique. A housing 568 may besecured to the support ring 502 of the stator 562 by, for example,press-fitting or threadly coupling the housing 568 to the support ring502, and may extend circumferentially about the shaft 566, the stator562, and the rotor 564.

The operation of the thrust-bearing apparatus 560 is discussed in moredetail with reference to FIG. 5B. FIG. 5B is a side cross-sectional viewin which the shaft 566 and housing 568 are not shown for clarity. Inoperation, lubrication fluid, drilling fluid, drilling mud, other fluid,or combinations thereof may flow between the shaft 566 and the housing568, and between the tilting pads 504 and the substantially continuousbearing element 548. More particularly, rotation of the rotor 564 at asufficiently high rotation speeds and/or sufficiently low thrust-loadsmay allow a fluid film 570 to develop between the bearing surfaces ofthe tilting pads 504 and the substantially continuous bearing surface.The fluid film 570 may develop under certain operational conditions inwhich the rotation speed of the rotor 564 is sufficiently great and thethrust-load is sufficiently low.

Under certain operational conditions, the pressure of the fluid film 570may be sufficient to substantially prevent contact between the superhardbearing surfaces of the tilting pads 504 and the substantiallycontinuous bearing surface and thus, may substantially reduce wear ofthe continuous bearing surface and the superhard bearing surfaces of thetilting pads 504. When the thrust loads exceed a certain value and/orthe rotation speed of the rotor 564 is reduced, the pressure of thefluid film 570 may not be sufficient to substantially prevent thebearing surfaces of the tilting pads 504 and the substantiallycontinuous bearing surface from contacting each other. Under suchoperational conditions, the thrust-bearing apparatus 560 is not operatedas a hydrodynamic bearing. Thus, under certain operational conditions,the thrust-bearing apparatus 560 may be operated as a hydrodynamicbearing apparatus and under other conditions the thrust-bearingapparatus 560 may be operated so that the superhard bearing surfaces ofthe tilting pads 504 and the continuous bearing element 548 contact eachother during use. As such, the superhard bearing surfaces of the tiltingpads 504 and/or substantially continuous bearing surface may comprisesuperhard materials that are sufficiently wear-resistant to accommodaterepetitive contact with each other, such as during start-up andshut-down of a system employing the thrust-bearing apparatus 560 orduring other operational conditions not favorable for forming the fluidfilm 570.

The concepts used in the thrust-bearing assemblies and apparatusesdescribed herein may also be employed in radial bearing assemblies andapparatuses. FIG. 6 is an exploded isometric view of a radial bearingapparatus 672, according to an embodiment. The radial bearing apparatus672 may include an inner race 664 (e.g., a runner or rotor). The innerrace 664 may include a support ring 650. The support ring 650 mayinclude an inner peripheral surface defining an hole 618 for receiving ashaft (not shown). The inner race 664 may also include a substantiallycontinuous bearing element 648 mounted to the support ring 650. Thesubstantially continuous bearing element 648 may include aconvexly-curved substantially continuous bearing surface 654 and may beformed from any of the materials previously discussed for use with thesubstantially continuous bearing element 448. The support ring 650 ofthe inner race 664 may include a circumferentially extending recess (notshown) that receives the substantially continuous bearing element 648.The continuous bearing element 648 may be secured within the recess orotherwise secured to the support ring 650 by brazing, press-fitting,using fasteners, or another suitable technique. Alternatively, the innerrace 664 may include a plurality of bearing elements (e.g., slidingbearing elements) secured to the support ring 650 instead of thecontinuous bearing element 648.

The radial bearing apparatus 672 may further include an outer race 662(e.g., a stator) configured to extend about and/or receive the innerrace 664. The outer race 662 may include a support ring 602 extendingabout a rotation axis 606. The outer race 662 may include a plurality ofcircumferentially-spaced tilting pads 604. The tilting pads 604 mayinclude any of the tilting pads or tilting pad features disclosed herein(e.g., tilting pads 104, 104A, 104B, 204, 304A′, 304A″, 304B, etc.). Forexample, the tilting pads 604 may include a superhard bearing element620 that includes a superhard table 608 defining a superhard bearingsurface 610. At least some of the superhard tables 608 may include athickness (e.g., maximum thickness) that is at least about 0.120 inchand/or two or more layers. Each of the superhard bearing surfaces 610may be substantially planar, although in other embodiments, each of thesuperhard bearing surfaces 610 may be a concavely-curved to generallycorrespond to the shape of convexly-curved substantially continuousbearing surface 654. Each tilting pad 604 may be tilted in a manner thatfacilities sweeping in of a lubricant or other fluid to form the fluidfilm between the inner race 664 and the outer race 662. Each tilting pad604 may be tilted and/or tilt about an axis that is generally parallelto the rotation axis 606. As a result, each tilting pad 604 may betilted at an angle relative to the inner and outer surfaces of thesupport ring 602 and in a circumferential fashion such that the leadingedges of the tilting pads 604 are about parallel to the axis 606.

Rotation of a shaft (not shown) secured to the inner race 664 may affectrotation of the inner race 664 relative to the outer race 662. Drillingfluid or other fluid or lubricant may be pumped between the superhardbearing surfaces 610 and the substantially continuous bearing surface654. As previously described with respect to the tilting padthrust-bearing apparatus 560, at a fluid film may develop between thesuperhard bearing surfaces 610 and the substantially continuous bearingsurface 654, and may develop sufficient pressure to maintain thesuperhard bearing surfaces 610 and the substantially continuous bearingsurface 654 apart from each other. Accordingly, wear on the superhardbearing surfaces 610 and the substantially continuous bearing surface654 may be reduced compared to when direct contact between superhardbearing surfaces 610 and the substantially continuous bearing surface654 occurs. It should be noted that in other embodiments, the radialbearing apparatus 672 may be configured as a journal bearing. In such anembodiment, the inner race 664 may be positioned eccentrically relativeto the outer race 662.

Any of the embodiments for bearing apparatuses discussed above may beused in a subterranean drilling system. FIG. 7 is a schematic isometriccutaway view of an embodiment of a subterranean drilling system 700according to an embodiment that uses a thrust-bearing apparatus. Thesubterranean drilling system 700 includes a housing 702 enclosing adownhole drilling motor 704 (i.e., a motor, turbine, or any other devicecapable of rotating an output shaft) that is operably connected to anoutput shaft 706. A thrust-bearing apparatus 708 is operably coupled tothe downhole drilling motor 704. The thrust-bearing apparatus 708 may beconfigured as any of the previously described thrust-bearing apparatusembodiments. A rotary drill bit 710 configured to engage a subterraneanformation and drill a borehole is connected to the output shaft 706. Therotary drill bit 710 is shown as so-called “fixed cutter” drill bitincluding a plurality of blades having a plurality of PDC cuttingelements 712 mounted thereon. However, in other embodiments, the rotarydrill bit 710 may be configured as a roller cone bit including aplurality of roller cones.

The thrust-bearing apparatus 708 includes a stator 714 that does notrotate and a rotor 716 that is attached to the output shaft 706 androtates with the output shaft 706. The stator 714 may include aplurality of circumferentially spaced tilting pads 718. For example, atleast some of the tilting pads 718 may include a superhard table (notshown) that exhibits a thickness (e.g., maximum thickness) that is atleast about 0.120 inch and/or at least two layers having different wearand/or thermal characteristics. The rotor 716 may include asubstantially continuous bearing element (not shown).

In operation, drilling fluid may be circulated through the downholedrilling motor 704 to generate torque and effect rotation of the outputshaft 706 and the rotary drill bit 710 attached thereto so that aborehole may be drilled. A portion of the drilling fluid may be used tolubricate opposing bearing surfaces of the stator 714 and rotor 716. Asthe borehole is drilled, pipe sections may be connected to thesubterranean drilling system 700 to form a drill string capable ofprogressively drilling the borehole to a greater depth within the earth.

The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting. Additionally, thewords “including,” “having,” and variants thereof (e.g., “includes” and“has”) as used herein, including the claims, shall be open ended andhave the same meaning as the word “comprising” and variants thereof(e.g., “comprise” and “comprises”).

The invention claimed is:
 1. A bearing apparatus, comprising a firstbearing assembly including: a first support ring; and a substantiallycontinuous bearing element secured to the first support ring, thesubstantially continuous bearing element including a substantiallycontinuous bearing surface; and a second bearing assembly including: asecond support ring; and a plurality of tilting pads distributedcircumferentially about the axis and tilted and/or tiltably securedrelative to the second support ring, each of the plurality of tiltingpads including a superhard table defining a superhard bearing surface,the plurality of tilting pads including at least one first tilting pad,the superhard table of the at least one first tilting pad includingpolycrystalline diamond exhibiting a thickness that is greater than0.120 inch.
 2. The bearing apparatus of claim 1, wherein the firstbearing assembly is a rotor and the second bearing assembly is a stator.3. The bearing apparatus of claim 1, wherein the substantiallycontinuous bearing element is formed from a single continuous bearingelement and the substantially continuous bearing surface is a continuousbearing surface.
 4. The bearing apparatus of claim 1, wherein thesubstantially continuous bearing element includes a plurality of bearingelements that collectively form the substantially continuous bearingelement.
 5. The bearing apparatus of claim 1, wherein the substantiallycontinuous bearing element includes polycrystalline diamond.
 6. Thebearing apparatus of claim 1, wherein the substantially continuousbearing element includes at least one of polycrystalline cubic boronnitride, silicon carbide, silicon nitride, tantalum carbide, tungstencarbide, boron carbide, reaction-bonded silicon nitride, orreaction-bonded silicon carbide.
 7. The bearing apparatus of claim 1,wherein the thickness of the superhard table of the at least one firsttilting is at least 0.156 inch.
 8. The bearing apparatus of claim 1,wherein the thickness of the superhard table of the at least one firsttilting is at least 0.200 inch.
 9. The bearing apparatus of claim 1,wherein the at least one first tilting pad includes a support plate andthe superhard table is secured, either directly or indirectly, to thesupport plate, and wherein the superhard bearing surface extends above atop surface of the support plate by a distance that is equal to orgreater than the thickness of the superhard table.
 10. The bearingapparatus of claim 9, wherein the distance is greater than about 0.18inch.
 11. The bearing apparatus of claim 1, wherein the superhard tableof the at least one first tilting pad includes a lower surface and atleast one peripheral surface extending between the superhard bearingsurface and the lower surface, the superhard table of the at least onefirst tilting pad including a lower layer extending from the lowersurface towards the superhard bearing surface and an upper layerextending from at least a portion of the superhard bearing surfacetowards the lower surface, the upper layer exhibiting a higher abrasionresistance than the lower layer.
 12. The bearing apparatus of claim 1,wherein the superhard table of the at least one first tilting padincludes a substantially uniform grain size therethrough.
 13. Thebearing apparatus of claim 1, wherein the plurality of tilting padsinclude at least one second tilting pad, the superhard table of the atleast one second tilting pad including polycrystalline diamondexhibiting a thickness that is less than 0.120 inch.
 14. The bearingapparatus of claim 1, wherein the plurality of tilting pads include atleast one second tilting pad, the superhard table of the at least onesecond tilting pad including a lower surface and at least one peripheralsurface extending between the superhard bearing surface and the lowersurface, the superhard table of the at least one second tilting padincluding a lower layer extending from the lower surface towards thesuperhard bearing surface and an upper layer extending from at least aportion of the superhard bearing surface towards the lower surface, theupper layer exhibiting a higher abrasion resistance than the lowerlayer.
 15. A bearing apparatus, comprising a rotor including: a firstsupport ring; and a substantially continuous bearing element secured tothe first support ring, the substantially continuous bearing elementincluding a superhard material defining a substantially continuousbearing surface; and a rotor including: a second support ring; and aplurality of tilting pads distributed circumferentially about the axisand tilted and/or tiltably secured relative to the second support ring,each of the plurality of tilting pads including a polycrystallinediamond table defining a superhard bearing surface, the polycrystallinediamond table of at least one of the plurality of tilting padsexhibiting a thickness that is greater than 0.200 inch.
 16. The bearingapparatus of claim 15, wherein the substantially continuous bearingelement is formed from a single continuous bearing element and thesubstantially continuous bearing surface is a continuous bearingsurface.
 17. The bearing apparatus of claim 15, wherein thesubstantially continuous bearing element includes a plurality of bearingelements that collectively form the substantially continuous bearingelement.
 18. The bearing apparatus of claim 15, wherein thepolycrystalline diamond table of the at least one of the plurality oftilting pads includes a lower surface and at least one peripheralsurface extending between the superhard bearing surface and the lowersurface, the polycrystalline diamond table of the at least one of theplurality of tilting pads including a lower layer extending from thelower surface towards the superhard bearing surface and an upper layerextending from at least a portion of the superhard bearing surfacetowards the lower surface, the upper layer exhibiting a higher abrasionresistance than the lower layer.
 19. The bearing apparatus of claim 15,wherein the substantially continuous bearing element includes at leastone of polycrystalline cubic boron nitride, silicon carbide, siliconnitride, tantalum carbide, tungsten carbide, boron carbide,reaction-bonded silicon nitride, or reaction-bonded silicon carbide. 20.The bearing apparatus of claim 15, wherein the superhard table of the atleast one of the plurality of tilting pads includes a lower surface andat least one peripheral surface extending between the superhard bearingsurface and the lower surface, the superhard table of the at least oneof the plurality of tilting pads including a lower layer extending fromthe lower surface towards the superhard bearing surface and an upperlayer extending from at least a portion of the superhard bearing surfacetowards the lower surface, the upper layer exhibiting a higher abrasionresistance than the lower layer.
 21. The bearing apparatus of claim 15,wherein the plurality of tilting pads include at least one secondtilting pad, the superhard table of the at least one second tilting padincluding polycrystalline diamond exhibiting a thickness that is lessthan 0.200 inch.